Blocking oscillator



July 29, 1952' v BESS 2,605,423

' BLOCKING OSCILLATOR Filed Feb. 5,1946:

VOLTAGE INVENTOR. LEON BESS ATTORNEY Patented July 29, 1952 UNI E S ATE- Q j I 2.

' BLOCKING OSCILLATOR Leon -Bess,-,Kansas i Mo-. assi h i', ne assignments, toathe United States of America 'as' representedbythe Secretary of the Navy Application February 5, 1946, Serial No. 645,621

This invention relates to blpckingoscillators and more specifically to a fast recovery cathode biasedblocking oscillator. I i

Theorthodox blocking oscillator has arelatively long recovery time determined, by the time constant of the resistor and capacitor combination used to cause blocking. When triggered operation is desired, thistime constant must ,be longer than the triggering interval to prevent self triggering. This necessitates a long time constant which leads to a degree of instability.-

The object of this present circuit is to eliminate the-above stated difiiculty by providing a cathode biased blocking oscillator'which hasa short time of recovery. 7, 7

,An additional object is toprovidea blocking oscillator employing a cathode follower to provide'the cathode bias.

A still further'object is to provide a cathode biasedblocking oscillator which will be stable in triggered operation.

These and other obj ectswill be apparent from the following specification when taken with the accompanying drawing, in which:

Fig. 1 is a diagram of the basic circuit of the invention; and

Fig. 2 shows certain waveforms which arise in the operation of the invention.

' In Fig. 1, the circuit consisting of electron tube I l, the source of plate potential B+, transformer I2, and the cathode bias system capacitor I3 and resistor I4; forms a. standard cathode biased blocking oscillator. In operation, this circuit will draw a single cycle of current-during which sufilcient bias will be. developed tokeep thecircuit inactive for a relatively long period of time. Output from the blocking oscillator may be taken from a winding of transformer [2 at terminal 2. For triggered operation, a trigger may be applied at the plate of electron tube ll through capacitor [5 from terminal I. Electron tube [0, in conjunction with the cathode bias system of the blocking oscillator, forms a cathode follower circuit with the grid returned to a fixed potential as determined by the voltage divider consisting of resistors I6 and I1.

Consider, in Fig. 1, the operation of the blocking oscillator circuit with electron tube It] removed. When electron tube ll starts to con-' duct, current flows through the center winding of transformer l2 inducing a positive potential on the winding connected to the grid. This increase in potential on the grid of electron tube II causes the tube to conduct more current and. the action is cumulative until the tube reaches ISCIaims. (crate-3' ,2 saturation. At-thls -;ti 1n the-current ceases to increase through the" center ;-wir,1 ding of transformer I2. andthe potential on the ,vvindingconnected to the grid drops toward zero. The drop in grid potential decreases the conduction of elec tron tube H, and again the action is cumulative. During this cycle of conductionby electron tube i, a char e was built up onhe th bias capacitor 13.; Thisohargeds of such polarity'as to make thecathode of electrontube'll (point 3) positive with respect to ground.- Atthe end of onecycle the ,g-rid ot electrontube H ,has turn d to round p tent a Whi e h ma h de isheld above gground bythecharge oncapacitor I3. This hasthe effe t,ot'keepingjelectron tube vI I from conducting and the tube will not conduct until. the charge on capacitor-I3 can be-removed y t f curr n h oush hesatho eles e tor I l. The otential; at point .3 will: decrease at an exponential rate as ;.show,n in Rig 2, curvea. The slope of thetrailing edge of this .curve .is determined by thecombination of; capacitor I 3 and resistor [4. This curve respresents the recovery time of the circuit. 'It-triggeredoperation is desired, the time oi recovery'must'be longer than the longest trigg ne -interval and -vo ta at hetimle eee ne.- .l e o -t e te ye e When electron tubev III is replaced -in the'circuit and theblocking oscillatorf res, acharge willbe built up qna ee i S b e se A 2 theisri of electron tube Illis at a;f ixed potential detern d by t e -.ve t ee widr res tor i and the rise in .pgtentialvat point-g will.-be-,.sufiici ent to cause electron tube 10 ito .ceas,e conduction. As capacitor l3 discharges through resistor I4, the potential at point 3 decreases until the relation between the grid and cathode potentials of electron tube It] is such as to cause tube In to become conducting. As the potential at point 3 decreases, the current through electron tube It! increases until an equilibrium point is reached. At this point the potential at point 3 will remain fixed as the current through electron tube -l 0 will equal the discharge current of capacitor I3. This final value of potential may be varied by varying the voltage divider resistors l6 and I! which determine the. grid potential of electron tube [0.

The presence of electron tube It allows the use of a smaller value of cathode resistor M or capacitor I3. This decreases the time required for the blocking oscillator circuit to recover. Fig. 2 curve b shows the cathode potential point 3 waveform with tube II) in place, and the values of V 1. A blocking oscillator comprising, a first electron tube including cathode, grid, and plate, a

source of plate potential, a transformer havin a first winding joining said plate and said source grid to" induce oscillation, a cathode bias system including said second tube for biasing said first tube, a capacitor shunting said bias system and charged by said oscillation to a potential biasing said tube to nonconduction, and means for applying a predetermined potential to said second tube grid to control said bias at a predetermined potential.

4. A blocking oscillator comprising, a first electron tube including a cathode, a grid and an anode, means for coupling a voltage change at said plate to said grid to induce oscillation, a single cathode bias resistor for biasing said tube,'a capacitor shunting said bias resistor and charged by said oscillation to a potential biasing said tube to nonconduction, a second electron and a second winding joining said grid and ground so connected as to couple a change in V voltage at said plate to said grid in inverse re-- to theca'thodeof said first electron tube, and

said grid being so biasedas to cause said second electron tube to become'conducting when said cathode is at a predetermined potential.

2, A blocking oscillator comprising, a first electron tube including cathode, grid and plate, a source of plate potential, a transformer having a first winding joining said source of plate potential and said plate, and a second winding joining said grid and ground, said windings being so poled as to couple a voltage change at said plate tofsaid-grid in inverse relationship, a cathode bias "system consisting of -a parallel combination of-a'- resistor and-capacitor, joining said cathode and ground, a second electron tube includingcathode, grid, and plate, said plate connectingto said source of plate potential, said cathode connecting to said cathode of said first electron tube, a voltage divider consisting of two resistors in seriesconnecting said source of plate potential and ground; said grid of said second electrontube connecting-to junction o f'said voltage dividing resistors,- said voltage divider determining potential of said grid which determines" potential ofsaid cathode at which said second electron tube becomes conducting.

3. A blocking oscillator comprising, first and second electron tubes including cathode, grid and plate electrodes, means for coupling a voltage change at said "first tube plate to-said first tube tube having its electron path connected to share said, cathode bias resistor, and means biasing said second electron tube to become conductin at a predetermined potential of said cathode to eontrolsaid first electron tube bias.

5. A blocking oscillator comprising, a first electron tube and having a cathode, a control grid-and a plate, a source of plate potential, a transformer having a first winding joining said plate on said source anda second winding joining said grid and ground so connected as to couple -a change in voltage at said plate to said grid in inverse relationship, a cathode bias system consisting of a parallel combination of a single resistor and a capacitor joining said cathode and ground, said capacitor being charged by the-conduction of said first tube to bias said first tube to nonconduction and being discharged by said resistor to render said tube conductive, a second electron tube including cathode, grid and plate, said plate connected to said source of plate potential, said cathode connected directly to the cathode of said first electron tube, said second tube being driven to cutoff by the action of said first tube, and means for biasing said second electron tube to become conducting when said cathodes are at a predetermined potential to control the bias potential applied to said first electron tube.

LEON BESS.

7 REFERENCES CITED I UNITED STATES PATENTS Number Name Date 2,221,452 Lewis Nov. 12, 1940 2,535,285 Heaton Dec. 26, 1950 

